This invention relates to a chain saw safety-brake system.
When a chain saw is operated to cut trees, for example, by moving a saw chain at high speed, the saw chain might produce a reaction if it is inadvertently brought into contact with a knot in the trunk or branch of a tree and the chain saw itself might be flung toward the operator in what is referred to as a kickback phenomenon. When this phenomenon occurs, the chain saw flung toward the operator by the reaction would cause a serious injury to the operator if it contacted the operator because the saw chain is in high-speed operation. This gives rise to the problem of how to prevent the occurrence of the kickback phenomenon which is a matter of life or death to the operator. To obviate this problem, proposals have been made to use various types of safety-brake system. Since the safety-brakes of the prior art for the chain saws are built in bodies of chain saws, difficulties have been experienced in adjusting or repairing, for example, the brake band and effecting maintenance of parts and replacing them by new ones after the safety-brakes have been assembled with the chain saws. Also, the brake handle has had its vibration amplified by the vibration of the engine of the chain saw, thereby causing the parts of the safety-brake including the brake band to vibrate at an inordinately high magnitude. In addition, even if the operator grips the handles of the chain saw firmly in normal operation, the brake might inadvertently be actuated when there is no need to apply the brake, thereby causing danger to the operator.